Regions behoeen the Rivers Lachlan and Darling. 131 



sandstone ajipears^ it is probable that the tertiary drift over- 

 lying it is not of great depth. 



The ^Tllole surfaee of this region is apparently composed of 

 tertiary drift ; but there is a marked differenee between the 

 open country and that covered with mallee. In the latter 

 limestone greatly abounds, and the ridges of red sand, already 

 mentionedj are always present, and come close up to the edge 

 of the open plains, but never enter them. The plains, on the 

 other hand, possess extensive tracts, having a surface of hard 

 blue claj'', and wide areas covered by a thin stratum of red 

 clay. Vast portions of the plains, however, have neither de- 

 scription of clay on their surface ; but, it is worthy of remark, 

 tliat where this is the case, water seems to have carried away 

 the clay stratum from the surface down into the absorbent 

 beds of lime-earth and limestone gravel beneath ; for such 

 places are always in hollows, or in great land depressions, and 

 a careful examination of the edges of them proves that this 

 alteration of the surface is a progressive change of a chemical 

 and mechanical character. There is a deep trench, destitute 

 of vegetation, on the one side of which is the clayey surface, 

 on the other, an extremely loose soil, like a level mass of re- 

 cently slaked lime, and standing higher than the original 

 sui'face. 



Thus the traveller in vain looks for water, even immediately 

 after rain, if he looks for it in the larger depressions of the sur- 

 face; for it is on the red clay, or on the blue clay tracts only, 

 that it is to be found in very shallow pools. This constitutes 

 the grand question for finding water on that level coimtry of 

 boundless plains — is the surface of red or blue clay ? But the 

 red is the most certain, for, being mixed with much red or 

 ferruginous sand, the surface does not crack so much as that 

 of the pure blue clay. 



It is highly interesting, I may here observe, to notice the 

 total change in the vegetation of the one surface from the 

 other; the clayey surface abounds with numerous varieties of 

 saltbush, but on the loose absorbent surface, where all the salts 

 have been carried deep into the earth, no saltbush grows; 

 nothing but herbs and a coarse grass, which produces a fine 

 large grain, not unlike French millet ; some of this seed I 

 have presented to Dr. Mueller, having found it in the crop of 

 a crested pigeon. The Doctor informs me that it is Pantcum 

 decomjjositum, from which the natives make bread. 



In reference to the diflereuce between the formation of the 

 plains and the malice country, one thing, I think, seems evi- 



K 2 



